Reflective webs of indeterminate length comprising reflective thermally transferable material, usually referred to as reflective hot stamp tapes, have heretofore been made in either one or two manners: (1) pigmentation has been provided entirely or almost entirely by conventional aluminum pigments or (2) a single continuous coated layer of metal has been incorporated therein, the metal being aluminum in almost every instance and being deposited by vapor deposition in vacuum.
The first has the advantage that it is cheap, abrasion-resistant and weather-resistant, but is lacking in mirror-type or bright reflectivity, having a diffuse reflectance of only about 5% at the maximum. The diffuse reflectance may be as low as 1.7%.
The second, on the other hand, has the advantage that it has higher diffuse reflectance but has the disadvantage that abrasion-resistance is low, even though a protective abrasion-resistant layer by provided; and weatherability is poor. Nonetheless, brightness is high, the diffuse reflectance being as high as 82%.
Both have the advantage of economy.
Attempts to merely utilize particles of McAdow in a hot stamp tape, without more, result in an unsatisfactory tape for the reasons discussed above in connection with the inadequacies of McAdow's particles.
Hot stamp tape may be made (3) with the platelets of the instant invention, in place of the aluminum particles of (1) or the layer of (2). Tape (3) has the advantage of moderately high diffuse reflectance (at least 15% to as high as 35%) coupled with excellent weatherability, excellent abrasion-resistance, excellent storage stability and heat stability and accordingly is believed to be unique, novel and inventive. It is theorized that the uniquely improved properties of (3) over (2) result from the fact that whereas in (2) the metal film is continuously, in (3) the metal component consists of a plurality of metal members separated from one another by reason of each metal member being a lamina in a discrete laminar platelet particle. Thus degradation or deterioration which starts from a nucleus in the metal and spreads rapidly therefrom, spreads easily throughout a large area of the film in a continuous film as in that of (2). Such degradation usually consists of oxidation by oxygen or chlorine which results in the film becoming transparent or translucent and ceasing to be reflective. However, in the structure of the instant invention, it appears that degradation spreading from a single nucleus can only spread through the single platelet particle in which the nucleus is located rather than through a larger area. Thus degradation in (2), spreading from only a few nuclei, can cover a very large area whereas, spreading from the same member of nuclei in (3), will involve only an area equal to the number of platelets containing the nuclei, which is a relatively insignificant area.
Despite these many advantages, tape (3) has the disadvantage that it is enormously expensive due to the very high cost of the platelets and due to the relatively low covering power of the platelets. Due to the many steps necessay to prepare the platelets they cost on the order of 200 to 300 times as much per pound as conventional aluminum pigment. Due to the further fact that a great deal of overlapping of platelets is necessary to provide sufficient coverage, the cost of providing a tape in accordance with (3) is far greater than that of tape (2). Thus, despite the marked advantages of (3), it is unfortunately prohibitively expensive.
However, yet, in accordance with another discovery we have made, we have found that we can provide all of the advantages of (3) at a cost not prohibitively greater than that of (1) or (2), for the same area by providing the structure (4) of the instant invention wherein a hot stamp tape is provided which incorporates optionally and preferably a protective layer together with a critically necessary layer comprising the platelets and a critically necessary underlying layer comprising standard aluminum pigment or equivalent.